For a long time now in the building trade, mixers for concrete, mortar, powders, dry and semi-dry granulates and similar conglomerate materials have been widely used, to prepare large volumes of such conglomerates, preferably intended to be loaded on vehicle-mounted concrete mixers, and subsequently cast. Examples of mixers are described in the European patent applications EP-A-1.685.933, EP-A-2.146.795 and EP-A-2.146.796 in the name of the present Applicant.
Mixers are known with a horizontal axis and with a vertical axis. In particular, traditional vertical axis mixers used comprise a circular mixing tank inside which one or more vertical rotatable arms operate, usually parallel, intended to mix the mixtures loaded into the tank. One example of a single rotatable vertical arm is described for example in document U.S.-A-2008/0130406. In particular, a plurality of plates, disposed radially with respect to the axial development of the support arm, are associated to the single rotatable vertical arm. The plates are suitably shaped to confer on the material a desired degree of mixing. However, this solution is particularly complex to make, and it is justified to use it only with small-size mixers, since the radial disposition of the plates causes great resistance to the rotation of the shaft, which is difficult to sustain for large quantities of material.
A mixer is also known, from DE-A-28.01.460, that comprises a plurality of blades mounted radially with respect to the rotatable vertical arm.
Each of the blades consists of a shank attached radially to the rotatable vertical arm. The shank is provided in its free end with a shaped mixing portion having two mixing walls reciprocally angled with respect to each other and both toward the rear part of the shank.
The shaped mixing portion is made in a single body with the shank, and is very thick so as to guarantee long duration of the blade despite wear phenomena.
This type of blade is particularly complex to make, they are heavy and not able to confer an adequate mixing action. Moreover, this form of embodiment is difficult to apply to mixers of the planetary type as described hereafter.
Solutions are also known in which each of the rotatable vertical arms carries at the lower end a mixing blade that is also disposed vertical and parallel to the axis of rotation of the rotatable vertical arms; in the course of the rotation of the respective arms, the blades are able to interfere effectively with the mixture to be amalgamated, repeatedly mixing and suitably amalgamating the components of the mixture loaded inside the tank. In this context, planetary mixers are known, in which the mixing blades rotate upon themselves and also around a vertical mixing arm, and which can be configured for example as a single, double or triple cross. Turbine mixers are also known, in which the mixing blades rotate only around a central mixing rotor and not on themselves. The mixing blades traditionally used, in particular for planetary and turbine mixers, have a shank intended to be attached to the respective vertical arm, and a mixing wall, inclined by a determinate blade inclination angle with respect to the shank and formed by symmetrical and tapered front mixing plates, on the right and left with respect to the axis of symmetry. In particular, the front mixing plates of the mixing wall define a so-called blade profile that is, over all, tapered toward the shank. In particular, the mixing blades are usually T-shaped, either with an axial symmetry along their main direction of development, so that the right and left front mixing plates of the mixing wall are equal with respect to the axis of symmetry, or with added material (in the front side), for example on the right, to improve the anti-wear material, giving a convex shape to the plane section of the blade.
The sum of the lengths of the tapered front mixing plates, right and left, corresponds to the overall length of the blade profile, while the sum of the height of the mixing wall and the shank represents the overall height of the mixing blade.
It is known that damage to the mixing blades in this type of mixer is usually due to phenomena of a mechanical nature, in particular abrasive and erosive wear, and also corrosive wear mechanisms, not negligible when the blades move in the mixture at speeds of more than 3.4 m/sec.
There is therefore a need to improve existing mixing blades, so as to reduce the effects of wear upon them.
Purpose of the present invention is to obtain a mixing blade that overcomes the disadvantages of the state of the art, in particular limiting the effects of wear.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.